The present invention relates to an antifouling coating composition, and more particularly to an antifouling coating composition for use with underwater structures such as ships, port facilities, buoys, pipelines, bridges, submarine stations, submarine oil field excavation facilities, water conduit raceway tubes in power plants, cultivating fishing nets, stationary fishing nets. Such coating composition is suitable for preventing underwater living things from adhering and growing on the surface of the underwater structure.
Biofouling, the growth of barnacles, seaweeds, tubeworms and other marine organisms on the hulls of ocean-going vessels, and other underwater structures, cause the international marine community billions of dollars a year. In the case of ocean-going vessels, most of this money goes for the extra fuel needed to overcome the increased drag on vessels. Some of it is spent for hull cleaning and repainting and for the upkeep on propulsion equipment.
One currently used hull antifouling coating contains species such as tributyltin compounds or copper oxide and function through leaching of the toxicant into the marine environment. The resulting environmental hazards of introducing such toxicants into the marine ecosystem include disruption of natural ecocycles for many commercially important shellfish and pollution of entire food chains. The removal and disposal of toxicant-containing coatings from ships and other structures also pose separate environmental hazards, driving up the cost of refurbishment.
An alternative approach is to use acrylic acid monomer compositions which are water soluble, i.e., a polyester resin with an acrylic acid group. Such coatings include a biocide, which after a certain amount of time becomes inactive. The composition, because it is water soluble, wears off over time, i e., is ablative, and exposes new and active biocide at the surface. Such a composition is known as a self-polishing composition. Thus the alternative approach has been to employ a polymeric coating to function as a fouling release coating. Poly(dimethylsiloxane) (xe2x80x9cPDMSxe2x80x9d)-based coatings have properties which meet some of those requirements. On the other hand, as noted, studies have shown that such a cured PDMS material becomes unstable when immersed in water for three months.
Another specific approach involves the use of a composition containing a majority by weight as resin-solid content a reaction-curable silicone resin composition, a silicone resin having the specific average molecular weight and viscosity and an alkoxy group at its molecular terminal. While such a composition exhibits non-toxic characteristics, it is silicone-based and in addition to the discussed disadvantages, subject to premature wear requiring frequent maintenance in the form of reapplication of the coating.
In accordance with the invention, an antifouling coating composition, which is a silicone modified glass, is provided which is extremely effective in preventing fouling, and which is highly durable over time. Also provided is a primer composition which is highly durable over time and permits a variety of antifouling compositions to be applied to various surfaces.
The antifouling composition of the present invention compromises a glassy matrix formed by crosslinking a mixture of a silanol-terminated silicone and an alkoxy-functionalized siloxane to provide an interpenetrating polymer network of glass and silicone and at least two materials capable of microphase separation, at least one of which is graftable to the glassy matrix.
The present invention also relates to a primer composition formed by crosslinking a mixture of an epoxy, an alkoxy-functionalized siloxane and a silane capable of compatabilizing the epoxy and the alkoxy-functionalized siloxane to provide an epoxy-modified interpenetrating polymer network of glass and epoxy.
The present invention also provides a method of treating a substrate to prevent fouling thereof. The method includes first applying to the substrate a primer composition formed by crosslinking a mixture of an epoxy, an alkoxy-functionalized siloxane and a silane capable of compatabilizing the epoxy and the alkoxy-functionalized siloxane to provide an epoxy-modified interpenetrating polymer network of glass and epoxy, and then applying a mixture of a silanol-terminated silicone and an alkoxy-functionalized siloxane, and at least two materials capable of microphase separation. Thereafter, the mixture is crosslinked to provide an interpenetrating polymer network of glass and silicone to which is grafted at least one of the materials capable of microphase separation. The crosslinking of the primer composition and the antifouling composition can occur substantially simultaneously using the same catalyst (e.g., titanium isopropoxide) or can occur separately.
Optionally the mixture/antifouling composition can include an agent capable of preventing or inhibiting slime (e.g., algae, bacteria, protozoa, diatoms, etc.) from growing on the surface of the coating. While in most cases, such agent will be included in the composition, there are instances when slime is not an issue, and the anti-slime agent can be omitted. Suitable agents capable of preventing or inhibiting slime include surfactants, emulsifiers, enzymes, silver compounds, quaternary amine compounds, sulfa-based antimicrobial compounds, saponin and cholesterol, and mixtures and blends thereof.
The present invention also provides a substrate such as a boat hull first coated with a primer composition formed by crosslinking a mixture of an epoxy, and alkoxy-functionalized siloxane and a silane capable of compatabilizing the epoxy and the alkoxy-functionalized siloxane to provide an epoxy-modified interpenetrating polymer network of glass and epoxy. The substrated includes a coated layer of an antifouling composition comprising a glassy matrix formed by crosslinking a mixture of a silanol-terminated silicone and an alkoxy-functionalized siloxane to provide an interpenetrating polymer network of glass and silicone; and at least two materials capable of microphase separation, at least one of which is graftable to the glass matrix.